The invention relates to a method for the production and/or conditioning of powdered material with the features mentioned in the preamble of claim 1 and the associated device having the features mentioned in the preamble of claim 9.
It is known to produce powdered material in a fluidized bed, in which a gas flow is supplied to maintain said fluidized bed. Here, the following types of operating a fluidized bed are known, which can be produced with the granulated or powdered material.
1. Spray Dryer
In a spray dryer, such as known from the patent publication DD 285 724 A5, a liquid containing solid materials is sprayed into the hot material-laden gas flow. Particles develop in the gas flow by way of drying, showing a hollow helical shape or fractions thereof. The material particles that develop have a relatively large grain size and usually show poor re-dispersing properties. A spray dryer according to the prior art is a very large and thus expensive apparatus, requiring a lot of space and large amounts of energy. Such spray dryers are not suitable to produce very small solid particles. An additional thermal conditioning of the particles produced in the spray dryer is impossible.
2. Fluidized Bed Arrangements with Inert Beds
Fluidized bed arrangements with inert beds, such as known from the U.S. Pat. No. 6,187,238, have a gas-permeable fluidized bed bottom. A fluidized material bed is formed by the gas supplied from the bottom via the fluidized bed bottom in which appropriate inert bodies are provided as well. However, no very fine particles with appropriately 100 μm can be produced here either, because the impulse acting on the inert particles is determined only by the predominantly vertical up and down motion of the inert particles in the given area of the fluidized bed, thus only between the fluidizing point and the discharge point and therefore it is insufficient for the requirement to produce fine particles from vaporized/evaporating liquids. In addition to drying the solid matter entrained in the introduced liquids on the surfaces of the inert bodies no additional thermal conditioning is possible in a fluidized bed stage.
3. Spray Towers with Fluidized Beds
Spray towers are known for example from the patent publication DD 272 576 A3, which are operated with a fluidized bed at their lower end. Here, the fluidized beds can be operated with or without any inert bodies. Here, thermal or mechanical post-conditioning by way of a respective abrasion of the particles falling from the spray tower is possible. It is disadvantageous here that during the thermal post-conditioning various gas flows are being mixed. In this combination the production of fine particles is also limited for the above-mentioned reasons.
4. Spouted Bed Arrangements
In an inert spouted bed stage the impulse potential to effect the inert particles is considerably greater than in a fluidized bed with equivalent inert bodies, because in the jet range the particle speed is considerably higher (e.g., 10 times higher) than the discharge speed of the particles and in spite thereof the particles are not removed due to the design typical for spouted bed arrangements. From the (patent publications DD 225 630 A1, DD 224 233 A1, DE 103 03 836 B4) spouted bed arrangements are known for the production of powdered material. Here, a gas flow is supplied from the bottom to the spouted bed arrangement at a high speed to create a vertically rotating spouted bed. A liquid containing solid matter is sprayed in, for example by one, two, or more spray nozzles from the bottom, the top, or the side of the jet chamber such that the liquid always wets the surfaces of the inert particles to the extent possible, i.e. that no overflow develops. The liquid containing solid matter, for example sediment, can also be added to the inert bed in motion via suitable conveyer devices, such as screws and/or slurry distributors, e.g., rotating wheels. Steel balls, ceramic balls, or Teflon particles having a suitable grain size, shape, surface condition, and density are used as inert particles provided in the spouted bed. The liquids are evaporated by the hot gas flow such that, on the one hand, dry material particles develop and material then develops on the inert particles, which adheres while drying. The material particles and the adhering dry solid matter is abraded by the inert particles moving in roller-shaped jets and are discharged from the jet chamber in the form of dust (e.g., <50 μm). The dust is usually removed as a product at one or more externally located, consecutively arranged different solid matter collectors of equal or different type (cyclones, filters.) Powdered products of increasingly smaller particle dimensions can be yielded, according to the capacity of the inert bed—spouted bed stage by the multiple consecutive arrangements of dust collectors downstream in reference to the spouted bed arrangement. It is disadvantageous that the desired small grain sizes are produced at minute amounts only. Additionally the consecutive arrangement of dust collectors is energy-consuming and thus expensive.